Although the practice of orthodontics can be traced back at least to the time of the Egyptian mummies, modern developments in the art began in the 1920's when Dr. Edward Angle developed the first edgewise bracket. Such a bracket is for the purpose of connecting an orthodontic archwire to a tooth, as opposed to simply wrapping wires around the tooth and ligating to an activating archwire as had been the practice previously. Later on the so-called twin bracket was developed by Swain to permit the use of the bracket to apply a greater rotating and torquing force to the tooth. Still later developments included the Lewis gull wing bracket, the Steiner spring wing bracket, and the Lang stiff wing which incorporated a hole for ligating to rotate the tooth.
Brackets for orthodontic use were originally hand made from gold. In the late 1930's brackets machined from stainless steel were introduced. Stainless steel is generally satisfactory as an orthodontic bracket material, but prior to the present invention has presented numerous problems. First, it has heretofore been necessary to individually machine each bracket. This is costly, and also results in highly angular edge surfaces which are very uncomfortable for the patient. Another difficulty involved the distinctive appearance of stainless steel, which many patients find objectionable.
In an attempt to overcome the foregoing and other difficulties, plastic orthodontic brackets were introduced. Plastic brackets can be fabricated so as to eliminate the angular edges of machined stainless steel brackets, and are therefore more comfortable for the patient. It is also possible to make plastic brackets in almost any desired color, including highly transparent brackets. It has been found in practice, however, that the use of polycarbonate plastic orthodontic brackets presents a different set of problems. First, plastic brackets are too weak to withstand desired torquing stresses, so that breakage and failure are not uncommon. Second, in the environment of the mouth plastic orthodontic brackets tend to rapidly discolor due to stains caused by various foods, tobacco, beverages such as tea and coffee, etc.
The present invention comprises improvements in the art of fabricating orthodontic appliances such as edgewise brackets, buccal tubes, and the like which overcome the foregoing and other difficulties long since associated with the prior art. In accordance with the broader aspects of the invention, orthodontic appliances are fabricated from either ceramic materials or metals utilizing an injection molding technique. Orthodontic appliances manufactured in accordance with the invention exhibit superior strength and toughness, are very comfortable for patients to use, are aesthetically pleasing, and do not stain or discolor in use.
Orthodontic appliances incorporating the invention are characterized by a domed outwardly facing surface. The domed outwardly facing surface is entirely curved in both the length and width dimensions, and is entirely free of angular edge surfaces.
In accordance with more specific aspects of the invention, orthodontic appliances may be fabricated from ceramic materials such as aluminum oxide. The color of each appliance can be made to correspond closely with the color of the tooth upon which the appliance will be used. Orthodontic appliances formed from ceramic materials are preferably adapted for bonding directly to the tooth surface. In such instances, the inwardly facing surface of the appliance may be scored to facilitate bonding, and may be provided with a noncircular aperture for receiving a quantity of bonding material and thereby preventing the appliance for rotating relative to the tooth, as the torquing forces are applied, via the rectangularly shaped wire. An aperture in the inwardly facing surface of the appliance may be formed with an undercut portion therein causing the bonding material and the appliance to be mechanically interlocked.